I've concluded that I can live without virtual desktops if I have some way to switch apps from the keyboard. Quickeys is the canonical way to do that on Apple systems, and they have a nice MacOS X port these days. Eighty dollars for yet another basic OS extension is a bit beyond my budget though. The shareware app Keyboard Maestro does much of what I need, and has stuff like a Windows-style Alt-Tab selector (by app, not document window, sorry) and multiple-clipboard handler in the licensed version. The lite version of it (what you get if you don't pay the measly $20) does pretty much everything I need, so I'm sticking with that.